1. Field of the Invention
The present invention pertains to catheters, and more particularly to catheters for cryosurgically treating tissue within the body of a patient.
2. Description of the Related Art
Cryosurgery has achieved wide acceptance in many fields of therapeutic medicine. For example, cryosurgical instruments have been used in the extraction of cataractous lenses of the eye, to freeze human tissue to effect necrosis, to form scar tissue, and to repair detached retinas. Examples of cryosurgical instruments are disclosed in U.S. Pat. Nos. 3,548,829; 2,664,344; and 4,039,102.
In recent years, cryosurgery has been employed to ablate particular regions of the heart during open heart surgery. Once the chest cavity of a patient has been opened to expose the heart, a hand-held cryoprobe is advanced to a particular region of the heart believed to be the cause of certain cardiac abnormalities such as arrhythmia. A super-cooled fluid is passed to the tip of the probe to destroy by rapid freezing the abnormal tissue adjacent the probe tip. Such cryosurgical treatment is advantangeous because it permits localized and highly specific tissue treatment. However, it can only be used during the course of open heart surgery. Despite recent advances, such open heart surgery is associated with considerable morbidity and mortality.
The management of patients with cardiac arrhythmia has posed a vexing clinical problem. Despite the recent introduction of several powerful anti-arrhythmic drugs, many arrhythmias for reasons yet unknown cannot be suppressed pharmacologically. Patients who do not respond to drug therapy develop an alarmingly high incidence of serious drug-induced side effects and are faced with the inconvenience and expense of taking medication several times a day. Alternative forms of antiarrhythmic therapy which have been recently developed, such as using pacemakers capable of terminating tachycardia, have proven successful in only a limited number of patients. Surgical ablation of some cardiac arrhythmias is also possible in some patients. However, this technique of treatment is associated with considerable morbidity and mortality due to the use of general anesthesia and cardiopulmonary bypass. Consequently, there is a need for a less surgically invasive, more acceptable form of treatment.
Since many cardiac arrhythmias arise from discrete, easily definable regions of the heart that are readily accessible during the course of cardiac catheterization, attention has recently turned to the possibility of ablating arrhythmogenic foci non-surgically using catheterization techniques. Delivery of high-energy DC electric shocks through intracardiac electrode catheters positioned fluoroscopically near the His bundle has been used successfully to produce A-V block in patients having rapid ventricular rates during refractory atrial fibrillation, atrial flutter or other supra-ventricular tachycardias. This same technique has been used to ablate accessory A-V pathways near the mouth of the coronary sinus in some patients suffering from Wolff-Parkinson-Wright syndrome. Unfortunately, the delivery of such high energy intracardiac shocks produces tissue damage that cannot be graded or accurately confined to a small area. This tissue damage may result in serious complications in some patients, and may even produce new arrhythmogenic foci.
Accordingly, it is an object of the present invention to provide a treatment for cardiac arrhythmias that is not accompanied by the problems attendant to previous forms of treatment.
It is another object of the present invention to provide a treatment for cardiac arrhythmias which is comparatively less invasive than other forms of treatment.
Yet another object of the present invention is to provide a treatment for cardiac arrhythmias that permits the identification and highly specific cyrogenic treatment of abnormal cardiac tissue.
Still yet another object of the present invention is to provide a catheter capable of ablating abnormal tissue located virtually anywhere in the body of a patient that is accessible through the circulatory system.